Comparative of diatom frustules, diatomite, and silica particles for constructing self-healing superhydrophobic materials with capacity for thermal energy storage

Introducing the capability of self-healing to superhydrophobic materials is an effective strategy for improving their durability. This study examined self-healing superhydrophobic coatings based on diatom frustules and paraffin wax, and systematically compared coatings based on diatom frustules with those prepared by using diatomite and synthesized silica. The diatom frustules had a much higher specific surface area (214.38 m2/g) and pore volume (0.97 cm3/g) than diatomite and synthesized silica, and thus only diatom frustule can provide sufficient micro/nanoscale roughness and adsorb a large number of low-surface-energy, healing agent paraffin wax to achieve self-healable superhydrophobicity. The superhydrophobic coatings thus obtained demonstrated the capability for repeated self-healing after heat treatment at 80 °C for 10 min when subjected to water jet-induced impact for 30 min as well as corrosion in 1 M NaOH and 1 M HCl for 4 h. As much as 60.66 % of paraffin wax was stored in the diatom frustules without leakage, much higher than the amounts in diatomite and synthesized silica. This helped ensure good thermal storage performance, with a melting enthalpy of 132.2 J/g and a freezing enthalpy of 127.9 J/g. Once equipped with the capacity for storing thermal energy, self-healing superhydrophobic materials can be used in a variety of applications that require thermal management, such as electronic devices, intelligent flexible textiles, and energy-efficient and self-cleaning buildings.